Using a network of small, automated telescopes known as HAT, Smithsonian astronomers have discovered a planet unlike any other known world. This new planet, designated HAT-P-1, orbits one member of a pair of distant stars 450 light-years away in the constellation Lacerta.
"We could be looking at an entirely new class of planets," said Gaspar Bakos, a Hubble fellow at CfA. Bakos designed and built the HAT network and is lead author of a paper submitted to the Astrophysical Journal describing the discovery
http://www.cfa.harvard.edu/previous/latest.html
With a radius about 1.38 times Jupiter's, HAT-P-1 is the largest known planet. In spite of its huge size, its mass is only half that of Jupiter.
"This planet is about one-quarter the density of water," Bakos said. "In other words, it's lighter than a giant ball of cork! Just like Saturn, it would float in a bathtub if you could find a tub big enough to hold it, but it would float almost three times higher."

Strange New Planet Baffles Astronomers

I'm sure Saturn still baffles them, too.

Posts moved into their own thread from this one, as I think the news is significant enough to deserve such treatment.

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Everything I need to know I learned through Googling.

Its already believed that the epistellar jovians suffer expansion because of superheating by the star along with constant bombardment by stellar winds venting its atmosphere. Its not beyond conception to think that a Saturnian type giant (one that was already lacking in density) migrated inward and poofed out larger.

Curious, though, why wasn't an atmospheric drop probe sent to Saturn with Cassini? You'd think with a less dense atmosphere, it could get deeper before crushing.

Money, mass, and Titan looked more interesting.

Fred

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"For shame, gentlemen, pack your evidence a little better against another time."
-- John Dryden, "The Vindication of The Duke of Guise" 1684

Touche`

"It’s lighter than a giant ball of cork" - Gaspar Bakos, Harvard-Smithsonian fellow.

http://www.msnbc.msn.com/id/14825910/


Position(2000): RA 22 57 46.83 Dec +38 40 29.8
magnitude 10.4

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`Irony` actually does mean `metal like`...

Problem is that HD 209458b and HAT-P-1 are larger than should, effects of warming included. Majority of known transiting planets *are not* nearly so puffed up, despite the fact that some of them are even hotter than these two. So there has to be additional sources of heating. Possibilities include an eccentric orbit (proven not to be true in the case of HD 209458b) and an Uranus-style tilted axis. In these cases the extra heat comes from tidal heating.

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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

From what I understood from some of the early studies, it was believed the epistellars were tidally locked, so you'd have a Uranus style barbeque of one half of the planet without the ridiculous axial tilt.

Maybe some of the denser epistellars aren't tidally locked, reducing some of the heating effects?

They can be tidally locked even if they don't rotate straight.

I have no idea how soon the "hot Jupiters" become tidally locked, but since they orbit so close their stars it must be relatively short time.

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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

Hrm. Imagine the storms those planets must have! All that energy, getting pumped into the atmosphere! What I wouldn't give for a close look.
... but not THAT close.

Also of note, a Uranian axial tilt wouldn't cause one side to superheat, since the tilt doesn't change as it orbits, so it would still enjoy "seasons" of about 8-12 hours in length when it would experience polar darkness.

Any chance bombardment could cause significant atmospheric heating? The system's age is a billion years younger than ours and this planet should be a big enough target.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

A star being a billion years younger would actually subject the planet to weaker bombardment. Stars get stronger as they get older.

In context with George's comment, it seems that you are saying that the Earth experienced less bombardment a billion years ago than it does today. Is that correct?

Title: HAT-P-1b: A Large-Radius, Low-Density Exoplanet Transiting one Member of a Stellar Binary
Authors: G. A. Bakos (1,2), R. W. Noyes (1), G. Kovacs (3), D. W. Latham (1), D. D. Sasselov (1), G. Torres (1), D. A. Fischer (6), R. P. Stefanik (1), B. Sato (7), J. A. Johnson (8), A. Pal (4,1), G. W. Marcy (8), R. P. Butler (9), G. A. Esquerdo (1), K. Z. Stanek (10), J. Lazar (5), I. Papp (5), P. Sari (5) B. Sipocz (4,1), ((1) CfA, (2) Hubble Fellow, (3) Konkoly Observatory, (4) Eotvos Lorand University, (5) Hungarian Astronomical Association, (6) San Francisco State University, (7) Okayama Astrophysical Observatory, (8) UC at Berkeley, (9) Carnegie, (10) Ohio State University)

Using small automated telescopes in Arizona and Hawaii, the HATNet project has detected an object transiting one member of the double star system ADS 16402 AB. This system is a pair of G0 main-sequence stars with age about 3 Gyr at a distance of ~139 pc and projected separation of ~1550 AU. The transit signal has a period of 4.46529 days and depth of 0.015 mag. From follow-up photometry and spectroscopy, we find that the object is a "hot Jupiter" planet with mass about 0.53 M_jup and radius ~1.36 R_jup travelling in an orbit with semimajor axis 0.055 AU and inclination about 85.9 deg, thus transiting the star at impact parameter 0.74 of the stellar radius. Based on a data set spanning three years, ephemerides for the transit centre are: T_C = 2453984.397 + N_tr * 4.46529. The planet, designated HAT-P-1b, appears to be at least as large in radius, and smaller in mean density, than any previously-known planet.

Read more (110kb, PDF)
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`Irony` actually does mean `metal like`...

Bah, misunderstood him, thought he meant bombardment as in stellar wind (crossed wire). My apologies.

That being said, the late bombardment period here was a lot longer than a billion years ago. More like less than a billion years AFTER the planets formed. Currently believed to have been triggered by Jupiter migrating inward to its current orbit. Prior to late heavy bombardment, the system had actually been rather quiet. Been pretty quiet since then, too.

As for heating from extensive bombardment in its system? Given that Jupiter took a comet on the chin with nary a flicker beyond cloud disruption, a gas giant would need to be utterly pulverized by material on a regular basis to heat up that much.

The problem with heating by that means is that its constantly adding mass to the planet, and unless its gaseous material, the heavy stuff would sink to the middle, and then you've got a nice and dense core with proportionally heavier gravity pulling the atmosphere down onto it.

I was not really advocating the bombardment idea too much, but this planet is very unusual and might need some unusual circumstances to explain its size.

However, after seeing the orbital radius of 0.055AU, it seems more likely its proximity to the G0 star would be the greatest likelyhood of causing atmospheric swelling.

If the G0 star had the same radiance as our G2 star, this planet will recieve ~450,000 watts per sq. meter of energy vs. our 1,367 w/m^2 [solar constant comparisson]. Since a G0 is a little hotter, the planet will receive even more energy.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

This was how the BBC reported it

But is it in hydrostatic equilibrium and has it cleared the path around it's orbit.

Well done to the team that found this

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Fame, glory adventure, a cyber warrior craves not these things.

It was still a fair question, and deserved a fair answer (once I actually recognized what was being questioned )